U.S. patent number 10,363,460 [Application Number 15/799,382] was granted by the patent office on 2019-07-30 for multi-piece solid golf ball.
This patent grant is currently assigned to Bridgestone Sports Co., Ltd.. The grantee listed for this patent is Bridgestone Sports Co., Ltd.. Invention is credited to Tsuyoshi Nakajima, Hideo Watanabe.
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United States Patent |
10,363,460 |
Watanabe , et al. |
July 30, 2019 |
Multi-piece solid golf ball
Abstract
In a multi-piece solid golf ball which includes a core of at
least one layer, a cover of at least one layer, and at least one
intermediate layer interposed between the core and the cover, the
cover is composed primarily of polyurethane and the following
parameters are controlled within specific ranges: core deflection,
melt flow rate of intermediate layer material, thickness of
intermediate layer, thickness and Shore D hardness of cover,
combined thickness of intermediate layer and cover, and the value
of (Shore D hardness of cover material)-(Shore D hardness of
intermediate layer material). This golf ball has a good, soft feel
at impact and lowers the rate of spin on full shots, achieving a
good distance.
Inventors: |
Watanabe; Hideo (Chichibushi,
JP), Nakajima; Tsuyoshi (Chichibushi, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgestone Sports Co., Ltd. |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Bridgestone Sports Co., Ltd.
(Minato-ku, Tokyo, JP)
|
Family
ID: |
62192900 |
Appl.
No.: |
15/799,382 |
Filed: |
October 31, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180147453 A1 |
May 31, 2018 |
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Foreign Application Priority Data
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Nov 29, 2016 [JP] |
|
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2016-231550 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B
37/0033 (20130101); A63B 37/0075 (20130101); A63B
37/0048 (20130101); A63B 37/0043 (20130101); A63B
37/0076 (20130101); A63B 37/0077 (20130101); A63B
37/0045 (20130101); A63B 37/0031 (20130101); A63B
37/0051 (20130101); A63B 37/0065 (20130101) |
Current International
Class: |
A63B
37/06 (20060101); A63B 37/00 (20060101) |
Field of
Search: |
;473/373,374 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003-190330 |
|
Jul 2003 |
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JP |
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3661812 |
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Jun 2005 |
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JP |
|
3861983 |
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Dec 2006 |
|
JP |
|
Primary Examiner: Gorden; Raeann
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. A multi-piece solid golf ball comprising a core of at least one
layer, a cover of at least one layer, and at least one intermediate
layer interposed between the core and the cover, wherein the core
has a deflection when compressed under a final load of 1,275 N (130
kgf) from an initial load state of 98 N (10 kgf) of at least 4.0
mm, the intermediate layer material has a melt flow rate (MFR) of
at least 2.5 g/10 min, the intermediate layer has a thickness of
from 1.0 to 1.8 mm, the cover is composed primarily of
polyurethane, the cover has a thickness of from 0.5 to 1.0 mm, the
cover has a Shore D hardness of at least 55, the sum of the
intermediate layer thickness and the cover thickness is not more
than 2.2 mm, and the value obtained by subtracting the Shore D
hardness of the intermediate layer material from the Shore D
hardness of the cover material is from -10 to 0, and wherein the
core is formed of a rubber composition comprising: (a) a base
rubber, (b) an .alpha.,.beta.-unsaturated carboxylic acid and/or a
metal salt thereof, (c) a crosslinking initiator, and (d) a metal
carboxylate in which the carboxylic acid bonded to metal is of two
or more different types and at least one of the carboxylic acids
has 8 or more carbon atoms, the component (d) being selected from
the group consisting of zinc monostearate monopalmitate, zinc
monostearate monomyristate, zinc monostearate monolaurate, zinc
monopalmitate monomyristate, zinc monopalmitate monolaurate, zinc
monostearate monoacrylate, zinc monostearate monomethacrylate, zinc
monostearate monomaleate, zinc monostearate monofumarate, zinc
monopalmitate monoacrylate, zinc monopalmitate monomethacrylate,
zinc monopalmitate monomaleate, zinc monopalmitate monofumarate,
zinc monomyristate monoacrylate, zinc monomyristate
monomethacrylate, zinc monomyristate monomaleate, zinc
monomyristate monofumarate, zinc monolaurate monoacrylate, zinc
monolaurate monomethacrylate, zinc monolaurate monomaleate and zinc
monolaurate monofumarate.
2. The golf ball of claim 1, wherein the intermediate layer
material has a Shore D hardness of from 62 to 67.
3. The golf ball of claim 1, wherein the ball has a surface
hardness, expressed in terms of Shore D hardness, of from 58 to
68.
4. The golf ball of claim 1, wherein the (cover
thickness)/(intermediate layer thickness) value is from 0.3 to
1.0.
5. The golf ball of claim 1, wherein the core has a deflection when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) of from 4.2 to 4.9 mm.
6. The golf ball of claim 1 wherein, letting CH be the deflection
of the core when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) and BH be the deflection of
the ball when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf), the value CH-BH is from 1.1
to 1.8 mm.
7. The golf ball of claim 1, wherein the value obtained by
subtracting the cover thickness from the intermediate layer
thickness is from 0.3 to 1.0 mm.
8. The golf ball of claim 1, wherein the upper limit of the melt
flow rate (MFR) of the intermediate layer material is 4.0 g/10
min.
9. The golf ball of claim 1, wherein an ionomer resin is used as
the intermediate layer material and the content of unsaturated
carboxylic acid (acid content) included in the intermediate layer
material is at least 10 wt %.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This non-provisional application claims priority under 35 U.S.C.
.sctn. 119(a) on Patent Application No. 2016-231550 filed in Japan
on Nov. 29, 2016, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
This invention relates to a multi-piece solid golf ball having at
least a three-layer construction that includes a core, an
intermediate layer and a cover.
BACKGROUND ART
Numerous golf balls having two or more cover layers formed over the
core, with the outermost layer made of a polyurethane-based
elastomer or other resin material composed primarily of
polyurethane, are available today on the market as golf balls for
professional golfers and skilled amateurs. Moreover, much art has
been described that attempts to, for example, increase the distance
traveled by multi-piece solid golf balls having three or more
pieces by optimizing the design (hardnesses, thicknesses, etc.) of
the ball structure and forming the outermost layer of a urethane
material.
For example, JP No. 3861983 describes a multi-piece solid golf ball
of three or more pieces wherein the resin material in the outermost
layer is formed of polyurethane, and parameters such as the
thickness of the intermediate layer are controlled. JP-A
2003-190330 is a golf ball with an inner/outer two-layer cover in
which a polyurethane elastomer is used as the primary material in
the outer cover layer and the Shore D hardnesses of the core
surface and the inner and outer cover layers are controlled. Also,
JP No. 3661812 describes a golf ball which has an inner/outer
two-layer cover, wherein the inner layer is hard and the outer
layer is soft.
However, these golf balls all have a somewhat hard feel on shots
with a driver (W#1) or are unable to increase the distance to an
adequate degree for mid-level amateur golfers and low head-speed
golfers. Hence, the) cannot be regarded as golf balls that are
fully satisfactory in terms of having both a good, soft feel at
impact and achieving an increased distance on full shots.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
golf ball which can achieve a distance on full shots with a driver
that will satisfy not only professional golfers and skilled
amateurs, but also mid-level golfers and low head-speed golfers,
and which moreover is capable of imparting a good, soft feel at
impact.
As a result of intensive investigations, the inventors have
discovered that, in a golf ball having a core, an intermediate
layer and a cover, by forming the cover (the outermost layer) of a
polyurethane resin material that is somewhat hard and controlling
within specific ranges the core deflection under specific loading,
the melt flow rate (MFR) of the intermediate layer material, the
thicknesses of the intermediate layer and cover, the Shore D
hardness of the cover, the sum of the intermediate layer thickness
and the cover thickness, and the value obtained by subtracting the
Shore D hardness of the intermediate layer material from the Shore
D hardness of the cover material, it is possible to impart such a
golf ball with a good, soft feel at impact while also lowering the
spin rate of the ball on full shots with a driver (W#1) and thereby
achieving a good distance, and it is moreover possible to obtain a
good scuff resistance even when the ball is struck with a grooved
wedge.
Accordingly, the invention provides a multi-piece solid golf ball
having a core of at least one layer, a cover of at least one layer,
and at least one intermediate layer interposed between the core and
the cover. The core has a deflection when compressed under a final
load of 1,275 N (130 kgf) from an initial load state of 98 N (10
kgf) of at least 4.0 mm, the intermediate layer material has a melt
flow rate (MFR) of at least 2.5 g/10 min, the intermediate layer
has a thickness of from 1.0 to 1.8 mm, the cover is composed
primarily of polyurethane, the cover has a thickness of from 0.5 to
1.0 mm, the cover has a Shore D hardness of at least 55, the sum of
the intermediate layer thickness and the cover thickness is not
more than 2.2 mm, and the value obtained by subtracting the Shore D
hardness of the intermediate layer material from the Shore D
hardness of the cover material is -10 or above.
In a preferred embodiment of the golf ball of the invention, the
intermediate layer material has a Shore D hardness of from 60 to
65.
In another preferred embodiment, the ball has a surface hardness,
expressed in terms of Shore D hardness, of from 58 to 68.
In yet another preferred embodiment, the (cover
thickness)/(intermediate layer thickness) value is from 0.3 to
1.0.
In still another preferred embodiment, the core has a deflection
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) of from 4.2 to 4.9 mm.
In a further preferred embodiment, letting CH be the deflection of
the core when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) and BH be the deflection of
the ball when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf), the value CH-BH is
preferably from 1.1 to 1.8 mm.
In an additional preferred embodiment, the value obtained by
subtracting the cover thickness from the intermediate layer
thickness is from 0.3 to 1.0 mm.
In yet another preferred embodiment, the core is formed of a rubber
composition that includes: (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid and/or a metal salt
thereof, (c) a crosslinking initiator, and (d) a metal carboxylate
in which the carboxylic acid bonded to metal is of two or more
different types and at least one of the carboxylic acids has 8 or
more carbon atoms.
Advantageous Effects of the Invention
The golf ball of the invention has a good, soft feel at impact and
lowers the rate of spin on full shots, achieving a good distance.
Moreover, this golf ball can obtain a good scuff resistance even
when hit with a grooved wedge.
BRIEF DESCRIPTION OF THE DIAGRAMS
FIG. 1 is a schematic cross-sectional view of a golf ball according
to one embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The objects, features and advantages of the invention will become
more apparent from the following detailed description taken in
conjunction with the appended diagram.
The multi-piece solid golf ball of the invention has, in order from
the inside thereof, a core, an intermediate layer and a cover. For
example, referring to FIG. 1, the golf ball G has a core 1, an
intermediate layer 2 encasing the core 1, and a cover 3 encasing
the intermediate layer 2. In addition, the golf ball typically has
numerous dimples D formed on the outer surface of the cover 3 in
order to enhance the aerodynamic properties. Each layer is
described in detail below.
The core is preferably made of a material that is composed
primarily of rubber. For example, use may be made of a rubber
composition obtained by compounding a base rubber as the primary
component, a crosslinking initiator, a co-crosslinking agent, an
inert filler and, optionally, an organosulfur compound.
Polybutadiene is preferably used as the base rubber. The
polybutadiene has a cis-1,4 bond content on the polymer chain of
typically at least 60 wt %, preferably at least 80 wt %, more
preferably at least 90 wt %, and most preferably at least 95 wt %.
When the content of cis-1,4 bonds among the bonds on the
polybutadiene molecule is too low, the resilience may decrease.
Rubber components other than this polybutadiene may be included in
the base rubber within a range that does not detract from the
advantageous effects of the invention. Examples of such rubber
components other than the foregoing polybutadiene include other
polybutadienes, and diene rubbers other than polybutadiene, such as
styrene-butadiene rubber, natural rubber, isoprene rubber and
ethylene-propylene-diene rubber.
An organic peroxide may be suitably used as the crosslinking
initiator. This organic peroxide is not particularly limited,
although the use of an organic peroxide having a one-minute
half-life temperature of between 110 and 185.degree. C. is
preferred. One, two or more organic peroxides may be used. The
content of organic peroxide per 100 parts by weight of the base
rubber is preferably at least 0.1 part by weight, and more
preferably at least 0.3 part by weight. The upper limit is
preferably not more than 5 parts by weight, more preferably not
more than 4 parts by weight, and even more preferably not more than
3 parts by weight. A commercial product may be used as the organic
peroxide. Specific examples include those available under the trade
names Percumyl D, Perhexa C-40, Niper BW and Peroyl L (all from NOF
Corporation), and Luperco 231XL (from Atochem Co.).
The co-crosslinking agent is exemplified by unsaturated carboxylic
acids and the metal salts of unsaturated carboxylic acids.
Illustrative examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred. Metal
salts of unsaturated carboxylic acids are not particularly limited,
and are exemplified by those obtained by neutralizing the foregoing
unsaturated carboxylic acids with the desired metal ions.
Illustrative examples include the zinc salts and magnesium salts of
methacrylic acid and acrylic acid. The use of zinc acrylate is
especially preferred.
These unsaturated carboxylic acids and/or metal salts thereof are
included in an amount per 100 parts by weight of the base rubber
which is typically at least 10 parts by weight, preferably at least
15 parts by weight, and more preferably at least 20 parts by
weight. The upper limit is typically not more than 60 parts by
weight, preferably not more than 50 parts by weight, more
preferably not more than 45 parts by weight, and most preferably
not more than 40 parts by weight. When too much is included, the
feel of the ball may become too hard and unpleasant. When too
little is included, the rebound may decrease.
In one embodiment of the core used in this invention, the core may
be formed of a rubber composition that includes: (a) a base rubber,
(b) an .alpha.,.beta.-unsaturated carboxylic acid and/or a metal
salt thereof, (c) a crosslinking initiator, and (d) a metal
carboxylate in which the carboxylic acid bonded to metal is of two
or more different types and at least one of the carboxylic acids
has 8 or more carbon atoms. These components (a), (b) and (c) are
the same as, respectively, the base rubber, the unsaturated
carboxylic acid and/or metal salt thereof, and the crosslinking
initiator described above.
Component (d) is described below.
(d) Metal Carboxylate
Component (d) is a metal carboxylate in which the carboxylic acid
bonded to metal is of two or more different types and at least one
of the carboxylic acids has 8 or more carbon atoms. As used herein,
"bond" refers to a bond between a metal and a carboxylic acid; the
number of bonds varies depending on the metal species.
Specifically, sodium and potassium have one bonding site, zinc and
calcium have two, and iron and aluminum have three. Because the
number of bonding sites on the metal must be two or more in order
for the metal carboxylate to be able to serve as component (d) in
this invention, the metal species is limited to those have two or
more bonding sites. In the case of a zinc salt, for example,
letting one of the two bonding sites on zinc be a carboxylic acid A
having 8 or more carbon atoms, the second carboxylic acid must be
one other than carboxylic acid A. Such carboxylic acids are denoted
herein with names having the prefix "mono" to distinguish them from
metal salts with two bonds (disalts) in which the carboxylic acids
bonded to the metal are both the same, such as zinc stearate.
Illustrative examples of component (d) include compounds of
structural formula (1) or (2) below. R.sup.1-M.sup.1-R.sup.2 (1) In
formula (1), R.sup.1 and R.sup.2 are each different carboxylic
acids, with at least one of R.sup.1 and R.sup.2 having 8 or more
carbon atoms. M.sup.1 represents a divalent metal atom.
##STR00001## In formula (2), R.sup.3 to R.sup.5 are two or more
different carboxylic acids, with at least one of R.sup.3 to R.sup.5
having 8 or more carbon atoms. M.sup.2 represents a trivalent metal
atom.
By having component (d) be two or more different carboxylic acids
bonded to a metal, with at least one of the carboxylic acids having
8 or more carbon atoms, the processability can be improved and the
decrease in the initial velocity of the core owing to the addition
of component (d) can be held to a minimum.
In component (d), it is preferable for at least one of the
carboxylic acids bonded to the metal to be an unsaturated
carboxylic acid, and more preferable for the unsaturated carboxylic
acid to be an .alpha.,.beta.-unsaturated carboxylic acid having
from 3 to 8 carbon atoms. Also, it is especially preferable for the
metal species in the metal carboxylate of component (d) to be one
selected from the group consisting of zinc, calcium, magnesium,
copper, aluminum, iron and zirconium.
Illustrative examples of component (d) include zinc monostearate
monopalmitate, zinc monostearate monomyristate, zinc monostearate
monolaurate, zinc monopalmitate monomyristate, zinc monopalmitate
monolaurate, zinc monostearate monoacrylate, zinc monostearate
monomethacrylate, zinc monostearate monomaleate, zinc monostearate
monofumarate, zinc monopalmitate monoacrylate, zinc monopalmitate
monomethacrylate, zinc monopalmitate monomaleate, zinc
monopalmitate monofumarate, zinc monomyristate monoacrylate, zinc
monomyristate monomethacrylate, zinc monomyristate monomaleate,
zinc monomyristate monofumarate, zinc monolaurate monoacrylate,
zinc monolaurate monomethacrylate, zinc monolaurate monomaleate and
zinc monolaurate monofumarate. Zinc monostearate monoacrylate is
preferred. Cases where the carboxylic acids bonded to the metal are
the same, such as zinc stearate, do not fall within the scope of
this invention.
The form of component (d) in the rubber composition is not
particularly limited. For example, it may be present in a form that
is mixed and dispersed, within the rubber composition, together
with the .alpha.,.beta.-unsaturated carboxylic acid or a metal salt
thereof serving as component (b). Another form is one in which the
surface of component (b), especially a metal salt of an
.alpha.,.beta.-unsaturated carboxylic acid such as zinc acrylate,
is coated with component (d). That is, component (d) may be
included in the rubber composition as a coating layer on component
(b).
Component (d) can be easily obtained by reacting a metal compound
in the presence of a plurality of carboxylic acids. Specifically,
in the case of zinc monostearate monoacrylate, this can be obtained
by dissolving stearate acid and acrylic acid in a reaction solution
and mixing therein zinc oxide suspended in a solvent so as to
induce the reaction. Alternatively, it can be obtained by adding
stearic acid and acrylic acid to a solution obtained by suspending
zinc oxide in a solvent.
The content of component (d) per 100 parts by weight of the base
rubber is preferably from 0.1 to 50 parts by weight, and more
preferably from 1 to 25 parts by weight. The weight ratio of
component (d) to component (b) is preferably from 1 to 99 wt %, and
more preferably from 4 to 50 wt %. At a component (d) content lower
than this range, a sufficient processability improving effect may
not be obtainable. On the other hand, at a component (d) content
higher than this range, the initial velocity of the core may
decrease more than necessary.
The core in this invention can be obtained by vulcanizing/curing
the above-described rubber composition by a method similar to that
used for conventional golf ball rubber compositions. Vulcanization
is carried out under conditions exemplified by a vulcanization
temperature of between 100 and 200.degree. C. and a vulcanization
time of from 5 to 40 minutes.
It is recommended that the core have a diameter of preferably at
least 38.3 mm, more preferably at least 38.4 mm, and even more
preferably at least 38.5 mm, with the upper limit being preferably
not more than 39.7 mm, more preferably not more than 39.3 mm, and
even more preferably not more than 39.0 mm. At a diameter smaller
than this, it may be difficult to obtain a sufficient spin
rate-lowering effect and resilience. On the other hand, at a
diameter larger than this value, a sufficient spin rate-lowering
effect may not be obtained and the advantageous effects imparted by
the cover may not be obtained.
The core has a deflection (mm) when compressed under a final load
of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which,
although not particularly limited, is to preferably from 4.0 to 5.1
mm, more preferably from 4.2 to 4.9 mm, and even more preferably
from 4.4 to 4.7 mm. When this value is too large, the resilience
may be too low, shortening the distance traveled by the ball, the
feel at impact may be too soft, and the durability of the ball to
repeated impact may worsen. On the other hand, when this value is
too small, the spin rate may rise excessively, possibly shortening
the distance traveled by the ball, and the feel at impact may be
too hard.
The core has a surface hardness Cs which, expressed in terms of
JIS-C hardness, is preferably from 68 to 80, more preferably from
70 to 78, and even more preferably from 72 to 76. When this MS-C
hardness value for the core surface hardness is too large, the feel
at impact may harden and the durability of the ball to cracking
under repeated impact may worsen. On the other hand, when this
value is too small, the resilience may become lower, possibly
shortening the distance traveled by the ball, and the durability of
the ball to repeated impact may worsen.
The core has a center hardness Cc which, expressed in terms of
JIS-C hardness, is preferably from 50 to 63, more preferably from
52 to 61, and even more preferably from 54 to 59. When this JIS-C
hardness value for the core center hardness is too large, the spin
rate may rise excessively, possibly shortening the distance
traveled by the ball and the feel at impact may become hard. On the
other hand, when this value is too small, the durability to
cracking on repeated impact may worsen and the feel at impact may
become too soft.
The hardness difference between the surface and center of the core,
i.e., the value Cs-Cc, is preferably from 10 to 26, more preferably
from 13 to 24, and even more preferably from 15 to 22. When this
hardness difference is too large, the durability of the ball to
cracking under repeated impact may worsen. On the other hand, when
this hardness difference is too small, the spin rate may rise
excessively, possibly shortening the distance traveled by the
ball.
The center hardness Cc is a cross-sectional hardness which refers
to the hardness measured at the center of the cross-section
obtained by cutting the core in half through the center. The
surface hardness Cs refers to the hardness measured at the
spherical surface of the core.
Next, the resin material used in the intermediate layer is
described.
The intermediate layer material is not particularly limited,
although an ionomer resin material or a highly neutralized resin
material is preferably used. Illustrative examples include
sodium-neutralized ionomer resins such as Himilan.RTM. 1605,
Himilan.RTM. 1601 and Surlyn.RTM. 8120; and zinc-neutralized
ionomer resins such as Himilan.RTM. 1557 and Himilan.RTM. 1706.
These may be used singly or two or more may be used together.
When an ionomer resin is used as the intermediate layer material,
the content of unsaturated carboxylic acid (acid content) included
in the intermediate layer material is generally at least 10 wt %,
and preferably at least 15 wt %, with the upper limit being not
more than 25 wt %, and preferably not more than 20 wt %. When the
acid content is low, the resilience decreases or the spin rate
increases, as a result of which a good distance may not be
obtained. When the acid content is high, the processability may
decrease or the durability to cracking under repeated impact may
worsen.
The melt flow rate (MFR) of the resin material used to form the
intermediate layer is adjusted within a specific range. That is,
the MFR of the resin material for the intermediate layer is at
least 2.5 g/10 mm, preferably at least 2.6 g/10 min, and more
preferably at least 2.7 g/10 min. It is recommended that the upper
limit be set to preferably not more than 5.0 g/10 min, and more
preferably not more than 4.0 g/10 min. When the melt flow rate is
too small, the processability may markedly decrease and the resin
material cannot be made to spread entirely around the core unless
the molding temperature is increased, as a result of which the
durability of the ball to cracking may worsen. The measurement
method involves measuring the resin flow rate at a test temperature
of 190.degree. C. and under a test load of 21.18 N (2.16 kgf) in
general accordance with JIS K-6760.
The surface of the intermediate layer formed from this intermediate
layer material is preferably abraded in order to increase adhesion
with the polyurethane used as the primary material of the
subsequently described cover. In addition, following such abrasion
treatment, it is preferable to either apply a primer (adhesive) to
the surface of the intermediate layer or to add an adhesion
promoter to the material.
The intermediate layer material has a specific gravity which is
generally less than 1.1, preferably from 0.90 to 1.05, and more
preferably from 0.93 to 0.99. At a specific gravity outside of this
range, the ball resilience decreases, as a result of which a good
distance may not be achieved, or the durability to cracking under
repeated impact may worsen.
The intermediate layer material has a hardness, expressed in terms
of Shore D hardness, which, although not particularly limited, is
preferably at least 56, more preferably at least 58, and even more
preferably at least 60, with the upper limit being preferably not
more than 67, more preferably not more than 65, and even more
preferably not more than 63. Also the sphere encased by the
intermediate layer (referred to below as the "intermediate
layer-encased sphere") has a surface hardness, expressed in terms
of Shore D hardness, which is preferably at least 62, more
preferably at least 64, and even more preferably at least 66, with
the upper limit being preferably not more than 73, more preferably
not more than 71, and even more preferably not more than 69. When
the intermediate layer material or intermediate layer-encased
sphere is softer than the respective above hardness ranges, the
ball is too receptive to spin on full shots, as a result of which a
good distance may not be achieved. On the other hand, when the ball
is harder than the above hardness range, the durability to cracking
on repeated impact may worsen, or the ball may have too hard a feel
at impact on shots with a putter or on approach shots.
The intermediate layer has a thickness which, although not
particularly limited, is preferably at least 1.0 mm, more
preferably at least 1.1 mm, and even more preferably at least 1.2
mm, with the upper limit being preferably not more than 1.8 mm,
more preferably not more than 1.6 mm, and even more preferably not
more than 1.5 mm. It is desirable for the intermediate layer to be
formed so as to be thicker than the subsequently described cover.
When the thickness of the intermediate layer falls outside of the
above numerical range or the intermediate layer is formed so as to
be thinner than the cover, the spin rate-lowering effect on shots
with a driver (W#1) is inadequate, as a result of which a good
distance may not be achieved.
Next, the cover serving as the outermost layer of the ball is
described.
The cover (outermost layer) material is not particularly limited;
various types of thermoplastic resin materials may be suitably
used. For reasons having to do with ball controllability and scuff
resistance, a polyurethane material is used as the primary material
of the cover. In particular, from the standpoint of the mass
productivity of the manufactured golf ball, it is preferable to use
a cover material composed primarily of a thermoplastic
polyurethane, with formation more preferably being carried out
using a resin blend in which the primary components are (O) a
thermoplastic polyurethane and (P) a polyisocyanate compound.
In the thermoplastic polyurethane composition containing above
components (O) and (P), to improve the ball properties even
further, a necessary and sufficient amount of unreacted isocyanate
groups should be present in the cover resin material. Specifically,
it is to recommended that the combined weight of above components
(O) and (P) be at least 60%, and more preferably at least 70%, of
the weight of the overall cover layer. Components (O) and (P) are
described below in detail.
The thermoplastic polyurethane (O) has a structure which includes
soft segments composed of a polymeric polyol (polymeric glycol)
that is a long-chain polyol, and hard segments composed of a chain
extender and a polyisocyanate compound. Here, the long-chain polyol
serving as a starting material may be any that has hitherto been
used in the art relating to thermoplastic polyurethanes, and is not
particularly limited. Illustrative examples include polyester
polyols, polyether polyols, polycarbonate polyols, polyester
polycarbonate polyols, polyolefin polyols, conjugated diene
polymer-based polyols, castor oil-based polyols, silicone-based
polyols and vinyl polymer-based polyols. These long-chain polyols
may be used singly, or two or more may be used in combination. Of
these, in terms of being able to synthesize a thermoplastic
polyurethane having a high rebound resilience and excellent
low-temperature properties, a polyether polyol is preferred.
Any chain extender that has hitherto been employed in the art
relating to thermoplastic polyurethanes may be advantageously used
as the chain extender. For example, low-molecular-weight compounds
with a molecular weight of 400 or less which have on the molecule
two or more active hydrogen atoms capable of reacting with
isocyanate groups are preferred. Illustrative, non-limiting,
examples of the chain extender include 1,4-butylene glycol,
1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and
2,2-dimethyl-1,3-propanediol. Of these, the chain extender is
preferably an aliphatic diol having 2 to 12 carbons, and more
preferably 1,4-butylene glycol.
Any polyisocyanate compound hitherto employed in the art relating
to thermoplastic polyurethanes may be suitably used without
particular limitation as the polyisocyanate compound. For example,
use may be made of one, two or more selected from the group
consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene
diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate,
xylylene diisocyanate, 1,5-naphthylene diisocyanate,
tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate,
dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, isophorone diisocyanate, norbornene
diisocyanate, trimethylhexamethylene diisocyanate and dimer acid
diisocyanate. However, depending on the type of isocyanate, the
crosslinking reactions during injection molding may be difficult to
control. In the practice of the invention, to provide a balance
between stability at the time of production and the properties that
are manifested, it is most preferable to use the following aromatic
diisocyanate: 4,4'-diphenylmethane diisocyanate.
Commercially available products may be used as the thermoplastic
polyurethane serving as component (O). Illustrative examples
include Pandex T-8295, T-8290, T-8283 and T-8260 (all from DIC
Bayer Polymer, Ltd.).
Although not an essential ingredient, a thermoplastic elastomer
other than the above thermoplastic polyurethane may be included as
an additional component together with components (O) and (P). By
including this component (Q) in the above resin blend, a further
improvement in the flowability of the resin blend can be achieved
and the properties required of a golf ball cover material, such as
resilience and scuff resistance, can be enhanced.
The relative proportions of above components (O), (P) and (Q) are
not particularly limited. However, to fully elicit the desirable
effects of the invention, the weight ratio (O):(P):(Q) is
preferably from 100:2:50 to 100:50:0, and more preferably from
100:2:50 to 100:30:8.
In addition to the ingredients making up the thermoplastic
polyurethane, various additives may be optionally included in the
above resin blend. For example, pigments, dispersants,
antioxidants, light stabilizers, ultraviolet absorbers and internal
mold lubricants may be suitably included.
The cover (outermost layer) has a material hardness, expressed in
terms of Shore D hardness, which, although not particularly
limited, is preferably at least 55, more preferably at least 56,
and even more preferably at least 57, with the upper limit being
preferably not more than 62, more preferably not more than 60, and
even more preferably not more than 58. Also, the surface hardness
of the cover-encased sphere, i.e., the surface hardness of the ball
as a whole, expressed in terms of Shore D hardness, is preferably
at least 61, more preferably at least 62, and even more preferably
at least 63, with the upper limit being preferably not more than
68, more preferably not more than 66, and even more preferably not
more than 64. When the surface hardness is softer than this range,
the spin rate on driver (W#1) shots or on full shots with an iron
becomes too high, as a result of which a good distance may not be
achieved. On the other hand, when the surface hardness is harder
than this range, on shots with a grooved wedge, the scuff
resistance may become poor or the feel on impact may become too
hard.
The cover (outermost layer) has a thickness which, although not
particularly limited, is preferably at least 0.5 mm, more
preferably at least 0.6 mm, and even more preferably at least 0.7
mm, with the upper limit being preferably not more than 1.0 mm,
more preferably not more than 0.9 mm, and even more preferably not
more than 0.8 mm. A cover that is thicker than this range may
result in an inadequate resilience and a higher spin rate on W#1
shots and shots with an iron, as a result of which a good distance
may not be obtained. On the other hand, when the cover is thinner
than the above range, the scuff resistance may worsen; in
particular, the feel at impact in the short game, such as on shots
with a putter, may become hard.
The cover (outermost layer)-encased sphere. i.e., the ball, has a
deflection (mm) when compressed under a final load of 1,275 N (130
kgf) from an initial load of 98 N (10 kgf) which, although not
particularly limited, is preferably from 2.4 to 3.7 mm, more
preferably from 2.6 to 3.5 mm, and even more preferably from 2.8 to
3.3 mm. When this value is too large, the feel at impact may be too
soft, the durability on repeated impact may worsen, or the initial
velocity on full shots may decrease, as a result of which the
intended distance may not be obtained. On the other hand, when this
value is too small, the feel at impact may become too hard or the
spin rate on full shots may become too high, as a result of which
the intended distance may not be obtained.
The manufacture of multi-piece solid golf balls in which the
above-described core, intermediate layer and cover (outermost
layer) are formed as successive layers may be carried out by a
customary method such as a known injection-molding process. For
example, a multi-piece golf ball may be obtained by placing, as the
core, a molded and crosslinked material composed primarily of a
rubber material in a given injection mold, injecting an
intermediate layer material over the core to give an intermediate
sphere, and subsequently placing the intermediate sphere in another
injection mold and injection-molding a cover (outermost layer)
material over the sphere. Alternatively, a cover (outermost layer)
may be formed over the intermediate layer by a method that involves
encasing the intermediate sphere with a cover, this being carried
out by, for example, enclosing the intermediate sphere within two
half-cups that have been pre-molded into hemispherical shapes, and
then molding under applied heat and pressure.
The golf ball of the invention preferably satisfies the following
conditions.
(I) Relationship Between Core Deflection and Ball Deflection Under
Specific Loading
The relationship between the core deflection and the ball
deflection under specific loading is optimized within a given
range. Letting CH be the deflection (mm) of the core when
compressed under a final load of 1,275 N from an initial load of
98N and BH be the deflection (mm) of the golf ball when compressed
under a final load of 1,275 N from an initial load of 98 N, the
value CH-BH is preferably from 1.0 to 2.0 mm, more preferably from
1.1 to 1.8 mm, and even more preferably from 1.2 to 1.6 mm. When
this value is too large, the durability to cracking under repeated
impact may worsen and the feel at impact on full shots may become
too soft. On the other hand, when this value is too small, the spin
rate on full shots may rise excessively, as a result of which the
intended distance may not be achieved.
(II) Thickness Relationship Between Intermediate Layer and
Cover
The relationship between the thickness of the intermediate layer
and the thickness of the cover is set within a given range. That
is, the value obtained by subtracting the cover thickness from the
intermediate layer thickness is preferably from 0 to 2.0 mm, more
preferably from 0.1 to 1.5 mm, and even more preferably from 0.3 to
1.0 mm. When this value is too large, the feel at impact may become
too hard or the core may become too soft, possibly resulting in a
poor durability to cracking on repeated impact. On the other hand,
when this value is too small, the spin rate on full shots may
become too high, as a result of which the intended distance may not
be obtained.
The sum of the intermediate layer thickness and the cover thickness
is preferably at least 1.6 mm, more preferably from 1.8 to 2.2 mm,
and even more preferably from 2.0 to 2.1 mm. When this combined
thickness is too large, the spin rate of full shots becomes too
large, as a result of which the intended distance cannot be
achieved. On the other hand, when this value is too small, the
durability on repeated impact may worsen.
In addition, the (cover thickness)/(intermediate layer thickness)
value is preferably from 0.3 to 1.0, more preferably from 0.4 to
0.8, and even more preferably from 0.5 to 0.7. When this value is
too large, the spin rate on full shots becomes too high, as a
result of which the intended distance may not be obtained. On the
other hand, when this value is too small, the scuff resistance may
be poor or the feel at impact may become too hard.
The value obtained by subtracting the Shore D hardness of the
intermediate layer material from the Shore D hardness of the cover
material is preferably from -10 to 0, more preferably from -8 to
-2, and even more preferably from -6 to -4. When this value is too
large, the scuff resistance may become poor. On the other hand,
when this value is too small, the spin rate on full shots may
become too high, as a result of which the intended distance may not
be obtained.
Numerous dimples may be formed on the outer surface of the cover
(outermost layer). The number of dimples arranged on the cover
surface, although not particularly limited, may be set to
preferably at least 280, more preferably at least 300, and even
more preferably at least 320, with the upper limit being preferably
not more than 360, more preferably not more than 350, and even more
preferably not more than 340. When the number of dimples is higher
than this range, the ball trajectory may become low, as a result of
which the distance may decrease. On the other hand, when the number
of dimples is lower than this range, the ball trajectory may become
high, as a result of which a good distance may not be achieved.
The dimple shapes that are used may be of one type or may be a
combination of two or more types selected from among circular
shapes, various polygonal shapes, dewdrop shapes and oval shapes.
When circular dimples are used, the dimple diameter may be set to
at least about 2.5 mm and up to about 6.5 mm, and the dimple depth
may be set to at least 0.08 mm and up to about 0.30 mm.
In order to fully manifest the aerodynamic properties, it is
desirable for the surface coverage ratio of dimples on the
spherical surface of the golf ball, i.e., the ratio SR of the sum
of the individual dimple surface areas, each defined by the flat
plane circumscribed by the edge of a dimple, with respect to the
spherical surface area of the ball were it to have no dimples
thereon, to be set to at least 60% and up to 90%. Also, to optimize
the ball trajectory, it is desirable for the value V.sub.0, defined
as the spatial volume of the individual dimples below the flat
plane circumscribed by the dimple edge, divided by the volume of
the cylinder whose base is the flat plane and whose height is the
maximum depth of the dimple from the base, to be set to at least
0.35 and up to 0.80. Moreover, it is preferable for the ratio VR of
the sum of the volumes of the individual dimples, each formed below
the flat plane circumscribed by the edge of a dimple, with respect
to the volume of the ball sphere were the ball surface to have no
dimples thereon, to be set to at least 0.6% and up to 1.0%. Outside
of the above ranges in these respective values, the resulting
trajectory may not enable a good distance to be obtained, and so
the ball may fail to travel a fully satisfactory distance.
The multi-piece solid golf ball of the invention can be made to
conform to the Rules of Golf for play. Specifically, the inventive
ball may be formed to a diameter which is such that the ball does
not pass through a ring having an inner diameter of 42.672 mm and
is not more than 42.80 mm, and to a weight which is preferably from
45.0 to 45.93 g.
EXAMPLES
The following Examples and Comparative Examples are provided to
illustrate the invention, and are not intended to limit the scope
thereof.
Examples 1 to 4, Comparative Examples 1 to 8
Formation of Core
Cores for each Working Example of the invention and each
Comparative Example were produced by preparing the rubber
compositions shown in Table 1 below, then molding and vulcanizing
the compositions under vulcanization conditions of 157.degree. C.
and 15 minutes.
TABLE-US-00001 TABLE 1 Core formulations Working Example
Comparative Example (pbw) 1 2 3 4 1 2 3 4 5 6 7 8 Polybutadiene A
50 50 50 50 50 50 50 50 50 50 50 50 Polybutadiene B 50 50 50 50 50
50 50 50 50 50 50 50 Unsaturated 25.3 23.3 25.3 23.3 25.3 31.5 25.3
25.3 25.3 25.3 25.3 23.3 metal carboxylate Metal carboxylate 1 3.9
3.9 Metal carboxylate 2 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9
Organic peroxide (1) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
0.3 Organic peroxide (2) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
0.3 0.3 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Barium sulfate 18.6 19.5 18.6 19.5 22.0 15.9 18.6 17.7 30.5 15.8
23.1 19.5- Zinc oxide 4 4 4 4 4 4 4 4 4 4 4 4 Zinc salt of 0.5 0.5
0.5 0.5 0.5 0.3 0.5 0.5 0.5 0.5 0.5 0.5 pentachlorothiophenol
Productivity good good Exc Exc good good good good good good good
good
Details on the ingredients shown in Table 1 are given below.
Numbers in the table indicate parts by weight. Polybutadiene A:
Available under the trade name "BR 51" from JSR Corporation
Polybutadiene B: Available under the trade name "BR 730" from JSR
Corporation Unsaturated metal carboxylate: Zinc acrylate (Wako Pure
Chemical Industries, Ltd.) Metal carboxylate 1: Zinc monoacrylate
monostearate (available from Nippon Shokubai Co., Ltd.) Metal
carboxylate 2: Zinc stearate (available from Wako Pure Chemical
Industries, Ltd.) Organic peroxide (1): Dicumyl peroxide, available
under the trade name "Percumyl D" from NOF Corporation Organic
peroxide (2): A mixture of 1,1-di(t-butylperoxy)cyclohexane and
silica, available under the trade name "Perhexa C-40" from NOF
Corporation Antioxidant: 2,2'-Methylenebis(4-methyl-6-butylphenol),
available under the trade name "Nocrac NS-6" from Ouchi Shinko
Chemical Industry Co., Ltd.
The core productivity for each Example was evaluated according to
the following criteria. The results are presented in the above
table.
Productivity
During mixing and extrusion of the rubber composition, the
following were evaluated: (i) mixing time, (ii) sticking to inner
wall of mixing apparatus, (iii) residue, (iv) coherence of rubber
composition following mixture, and (v) surface roughness of rubber
composition when extruded. These were judged collectively as being
indicative of very high productivity (Exc), high productivity
(Good), or low productivity (NG).
Formation of Intermediate Layer and Cover
Next, the intermediate layer and the cover were successively
injection-molded from the blends of resin materials I to V shown in
Table 2 below over the core obtained above, thereby producing
three-piece solid golf balls. Although not shown in the diagram, a
common dimple pattern was formed on the surface of the ball in each
Working Example and Comparative Example.
TABLE-US-00002 TABLE 2 Cover formulations (pbw) Intermediate layer
I II III IV V T-8295 100 T-8290 100 Himilan .RTM. 1706 35 50
Himilan .RTM. 1557 15 Himilan .RTM. 1605 50 50 Himilan .RTM. 1855
50 Himilan .RTM. 1601 50 Hytrel .RTM. 4001 11 11 Titanium oxide 3.9
2.1 3.9 Polyethylene wax 1.2 1.2 Isocyanate compound 7.5 7.5
Trimethylolpropane 1.1 Magnesium stearate 1 MFR (g/10 min).sup.1)
2.7 NM.sup.2) 1.1 NM.sup.2) 1.9 .sup.1)Melt flow rate (MFR) values
in the table were measured based on JIS K-6760. .sup.2)NM = not
measurable. The value was too large to be measured.
Trade names and other details on the materials shown in Table 2 are
as follows. T-8290, T-8295: MDI-PTMG type thermoplastic
polyurethanes available from DIC Bayer Polymer under the trademark
Pandex. Himilan.RTM.: Ionomers available from DuPont-Mitsui
Polychemicals Co., Ltd. Hytrel.RTM.: A thermoplastic polyether
ester elastomer available from DuPont-Toray Co., Ltd. Polyethylene
wax: Available as "Sanwax 161P" from Sanyo Chemical Industries,
Ltd. Isocyanate compound: 4,4'-Diphenylmethane diisocyanate
For each of the golf balls obtained, properties such as the
cross-sectional hardness of the core, the core diameter, the
thickness and material hardness of each layer, and the surface
hardness of each encased sphere were evaluated by the following
methods. The results are shown in Table 3.
Diameter of Core and Intermediate Layer-Encased Sphere
The diameters at five random places on the surface were measured at
a temperature of 23.9.+-.1.degree. C. and, using the average of
these measurements as the measured value for a single core or
intermediate layer-encased sphere, the average diameter for five
measured to cores or intermediate layer-encased spheres was
determined.
Ball Diameter
The diameters at five random dimple-free areas on the surface of a
ball were measured at a temperature of 23.9.+-.1.degree. C. and,
using the average of these measurements as the measured value for a
single ball, the average diameter for five measured balls was
determined.
Deflection of Core and Ball
A core or ball was placed on a hard plate and the amount of
deflection when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) was measured. The amount of
deflection here refers in each case to the measured value obtained
after holding the test specimen isothermally at 23.9.degree. C.
Center and Surface Hardnesses of Core (JIS-C Hardness)
The core center hardness was obtained by cutting the core in half
through the center and measuring the hardness at the center of the
resulting cross-section. The core surface hardness was obtained by
perpendicularly pressing the indenter of a durometer against the
surface of the spherical core and measuring the hardness. Both
hardnesses are measured with the spring-type durometer (JIS-C
model) specified in JIS K 6301-1975.
Surface Hardnesses of Intermediate Layer-Encased Sphere and Ball
(Shore D Hardness)
Measurements were taken by pressing the durometer indenter
perpendicularly against the surface of the intermediate
layer-encased sphere or of the ball (i.e., the surface of the
cover). The surface hardness of the ball (cover) is the measured
value obtained at dimple-free places (lands) on the ball surface.
The Shore D hardnesses were measured with a type D durometer in
accordance with ASTM D2240-95.
Material Hardnesses of Intermediate Layer and Cover (Shore D
Hardness)
The intermediate layer-forming and cover-forming resin materials
were molded into sheets having a thickness of 2 mm and left to
stand for at least two weeks, following which the Shore D
hardnesses were measured in accordance with ASTM D2240-95.
TABLE-US-00003 TABLE 3 Working Example Comparative Example 1 2 3 4
1 2 3 4 5 6 7 8 Construction 3- 3- 3- 3- 3- 3- 3- 3- 3- 3- 3- 3-
piece piece piece piece piece piece piece piece piece piece piece
piece Core Diameter (mm) 38.5 38.5 38.5 38.5 38.5 38.5 38.5 39.3
37.7 39.5 37.1 38.5 Weight (g) 34.8 34.8 34.8 34.8 35.3 34.8 34.8
36.8 34.5 37.0 31.8 34.8 Specific gravity 1.163 1.163 1.163 1.163
1.182 1.163 1.163 1.158 1.229 1.- 147 1.188 1.163 Deflection (mm)
4.3 4.6 4.3 4.6 4.3 3.2 4.3 4.3 4.3 4.3 4.3 4.6 Surface JIS-C 75 73
74 72 75 79 75 75 75 75 75 73 hardness (Cs) Center JIS-C 58 55 57
55 58 66 58 58 58 58 58 55 hardness (Cc) Surface - Center 17 18 17
17 17 13 17 17 17 17 17 18 (Cs - Cc) Inter- Type of material I I I
I I I I I I I I V mediate Thickness (min) 1.3 1.3 1.3 1.3 1.3 1.3
1.3 1.3 1.3 0.8 2.0 1.3 layer Specific gravity 0.95 0.95 0.95 0.95
0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 Shore D hardness 62 62 62
62 62 62 62 62 62 62 62 63 of material Inter- Diameter (mm) 41.1
41.1 41.1 41.1 41.1 41.1 41.1 41.9 40.3 41.1 41.1 41.1 mediate
Weight (g) 40.9 40.9 40.9 40.9 41.5 40.9 40.9 43.2 38.6 40.9 40.9
40.9 layer- Shore D hardness 68 68 68 68 68 68 68 68 68 68 68 69
encased at surface sphere Cover Type of material II II II II III I
IV II II II II II Thickness (mm) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.4
1.2 0.8 0.8 0.8 Specific gravity 1.12 1.12 1.12 1.12 0.98 1.12 1.12
1.12 1.12 1.12 1.12 1- .12 Shore D hardness 57 57 57 57 57 57 50 57
57 57 57 57 of material Ball Diameter (mm) 42.7 42.7 42.7 42.7 42.7
42.7 42.7 cover 42.7 42.7 42.7 42.7 Weight (g) 45.5 45.5 45.5 45.5
45.5 45.5 45.5 layer 45.5 45.5 45.5 45.5 Deflection (mm) 2.9 3.1
2.9 3.1 2.9 2.3 3.0 could 3.2 3.0 2.7 3.0 Shore D hardness 63 63 63
63 63 63 56 not be 62 63 63 63 at surface injec- Cover material
hardness - -5 -5 -5 -5 -5 -5 -12 tion- -5 -5 -5 -6 Intermediate
layer material molded hardness (Shore D) (could Ball surface
hardness - -5 -5 -5 -5 -5 -5 -12 not be -6 -5 -5 -6 Intermediate
layer surface formed) hardness (Shore D) Intermediate layer
thickness - 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.1 0 1.2 0.5 Cover
thickness (mm) Cover thickness/Intermediate 0.62 0.62 0.62 0.62
0.62 0.62 0.62 0.92 1.00- 0.40 0.62 layer thickness Core deflection
- 1.4 1.5 1.4 1.5 1.4 0.9 1.3 1.1 1.3 1.6 1.6 Ball deflection (mm)
Cover thickness + Intermediate 2.1 2.1 2.1 2.1 2.1 2.1 2.1 -- 2.5
1.6 2.8 2.1 layer thickness (mm)
The flight performance, feel at impact, scuff resistance and
durability of each golf ball were evaluated by the following
methods. The results are shown in Table 4. These measurements were
all carried out in a 23.degree. C. environment.
Flight Performance
A driver (W#1) was mounted on a golf swing robot, the distance
traveled by the ball when struck at a head speed (HS) of 40 m/s was
measured, and the flight performance was rated according to the
criteria shown below. The club used was the J715 B3 (2014 model)
manufactured by Bridgestone Sports Co., Ltd. The spin rate of the
ball immediately after being struck was measured with an apparatus
for measuring the initial conditions.
Rating Criteria: Good: Total distance was 190.0 m or more NG: Total
distance was less than 190.0 m Feel of Ball
The balls were hit with a driver (W#1) by amateur golfers having
head speeds of 35 to 45 m/s, and sensory evaluations were carried
out under the following criteria.
Rating Criteria: Good: Six or more of the ten golfers experienced a
good feel at impact Fair: Three to five of the ten golfers
experienced a good feel at impact NG: Two or fewer of the ten
golfers experienced a good feel at impact Scuff Resistance
A non-plated pitching sand wedge was set in a swing robot and the
ball was hit once at a head speed (HS) of 35 m/s, following which
the surface state of the ball was visually examined and rated as
follows.
Rating Criteria: Good: The ball can still be used. NG: The ball can
no longer be used. Durability
The balls in the respective Examples were repeatedly struck at a
head speed (HS) of 40 m/s with a driver (W#1). The durability index
in each Example was calculated relative to an arbitrary index of
100 for the number of shots at which the ball in Example 2 began to
crack, and the durability was rated according to the following
criteria.
Rating Criteria: Good: Durability index was 95 or more NG:
Durability index was less than 95
TABLE-US-00004 TABLE 4 Working Example Comparative Example 1 2 3 4
1 2 3 5 6 7 8 Flight W#1 Spin rate 2,735 2,650 2,730 2,630 2,788
2,855 2,865 2,839 2,829 2,810 2,630 perfor- HS, (rpm) mance 40 m/s
Total distance 192.9 192.0 193.1 192.5 192.3 192.6 189.3 189.7
189.8 191.5 192.- 4 (m) Rating good good good good good good NG NG
NG good good Feel at impact Rating good good good good good NG good
good good fair good- Scuff resistance Rating good good good good NG
good good good good good go- od Durability to Rating good good good
good good good good good NG good NG repeated impact
As is apparent from the results in Table 4, the golf balls in
Comparative Examples 1 to 8 were inferior in the following way to
the golf balls of the invention that were obtained in the Working
Examples.
In Comparative Example 1, the cover material was made of an
ionomer, and thus had a poor scuff resistance.
In Comparative Example 2, the core deflection was small (meaning
that the ball was hard), and so the feel at impact was poor.
In Comparative Example 3, because the cover hardness was too low
and the value obtained by subtracting the intermediate layer
material hardness from the cover material hardness is lower (more
negative) than -10, the ball was too receptive to spin on shots
with a driver (W#1), as a result of which a good distance was not
obtained.
In Comparative Example 4, injection molding targeted at a cover
thickness of 0.4 mm was attempted, but the resin material did not
spread properly within the mold cavity, as a result of which
complete molding of the ball was not possible.
In Comparative Example 5, the cover thickness was too large and the
sum of the intermediate layer thickness and the cover thickness
exceeded 2.3 mm, as a result of which the ball was too receptive to
spin on driver (W#1) shots and a good distance was not
obtained.
In Comparative Example 6, the intermediate layer was too thin, as a
result of which the spin rate on shots with a driver (W#1)
increased and a good distance was not obtained. In addition, the
durability to repeated impact was poor.
In Comparative Example 7, the intermediate layer was too thick, in
addition to which the sum of the intermediate layer thickness and
the cover thickness exceeded 2.3 mm, and so the feel at impact was
poor.
In Comparative Example 8, the intermediate layer material had a
melt flow rate of less than 2.5 g/10 min and the durability to
cracking on repeated impact was poor.
Japanese Patent Application No. 2016-231550 is incorporated herein
by reference.
Although some preferred embodiments have been described, many
modifications and variations may be made thereto in light of the
above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
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